Manufacture of concentrated nitric acid



E. BEPIGVE AND 0. JENSEN.

MANUFACTURE 0F CONCENTRATED NITRIC ACID. APPLICATION FILED SEPT. so,I9I.

1,338,4 1 '7, i Patented Apr. 27, 1920.

,may H20/7 (11g/gel z/ C 071/0 (ntl 1; taf? Hl@ I UNITED sTATEs PATENToEEicE.

EINAR BERGVE. OF NOTODDEN, AND OLAF- JENSEN, OF CHRISTIANIA, NORWAY,

ASSIGNORS TO NORSK HYDRO-ELEKTRISK KVAELSTOFAKTIESELSKAB, OF

CHRISTIANIA, NORWAY.

MANUFACTURE OF CONCENTRATED NITRIC ACID.

App1ication^1ed September 30, 1918.. Serial No. 256,249.

To all whomzt may concern:

Be it known that we, EINAR BERGVE and OLAF JENSEN, subjects of theKing.. of Norway, of Notodden, Norway, and Christiania,

`Norway, respectively, have in vented certain- Specication of LettersPatent.

new and useful Improvements in the-Manu` clear, and exact description ofthe invention,

such as-will enable others skilled in the art to which it appertains tomake and use the same, reference being had to the accompanying drawings,and to letters or iigures of reference marked thereon, which form aVpart of this specification.

This invention relates to the manufactur of concentrated nitric acidfrom nitrogen oxids andhas for its object an improved process forcarrying such manufacture into eect.

For the purpose of producing concentrated'nitric acid from such nitrousgases as are obtained in processes of oxidizing nitrogen two methodshave been tried. According to the one of these methods the gases havebeen absorbed in water so as to obtain dilute' nitric acid, whichthereupon by a concentration process has been converted intoconcentrated or highly `concentrated nitric acid. This process can becarried out in a continuous manner but requires the use of a rathercomplicated apparatus.

According to the second method, which has.

been suggested nitrogen peroxid is pro lduced from the gases' and isthen (prefer,n

ably in a liquid state) treated in an autoclave under a high pressurewith an equimolecular quantity ofwater and oxygen the result aimed atthereby being to obtain highly concentrated nitric acid.I The4experiments which have been made tosolve the problem in this mannerhave beeny based upon discontinuous,processes. "3

This latter.; circumstance kas well as the fact that thesuggestedprocesses which have `been based' upon' this principle require apreceding conversion of the produced nitro* gen oxidsintofnitrogengperoxid involving an unsatisfactory utilizationof theoxygen have prevented the processes from coming into\ practical use. y r

. According to the present invention, which is based upon a continuousworking,

Patented Apr. 27, 19,20.

.concentrated nitric acid is obtained directly from' gaseous nitrogenoxid and' nitrogen tetroxid (peroxid) by means of subjecting -thesegases to" the action of oxygen under (pressure in a system of apparatuscomprising two or more scrubbers in which the mixture of oxygenand thesaid gases come into lcontact Vwith water or dilute nitric acidrespectively. This method requires an apparatus of a comparativelysimpleconstruction and the oxygen necessary for the process is used toestablish a circulation of the reaction liquid in the various sectionsof the apparatus. The oxygen is caused to remain as long as possible incontact with the liquid, the oxygen and liquid being moved in the samedirection through the sections of the plant-where the reaction takesplace while the oxygen to obtain the best possible utilization of thesameis moved in counter current to the liquid when the plant isconsidered as a unit.

A suitable method, of carrying the invention into effect is described inthe following, reference being had to the accompanying drawing.

In the illustrated example the process is carried out in two Steps.Nitrogen tetroxid and water or dilute nitric acid are mixed in theY-shaped pipe system m and the mixture flows through the pipe L downinto a pneumatic liquid raiser E operated by oxygen introduced throughthe pipe H. The pneumatic liquid raiser causes the mixture to flowthrough the pipe I to the top of the tower A which is lfilled withpieces of quartz I -tom of the tower a portion of' the liquidl or other'suitable material. From the botis returned through the pipe D to theraiser E, while another portion flows through the siphon C and pipe G tothe pneumatic liquid raiser E', which is also operated by oxygen.

' This oxygen is supplied (from a compressor not shown) through the pipeD. This raiser causes the mixture to pass vto the top of the tower B.From the bottom of this tower4 a portion of the liquid .is returned bythe pipe Mto the raiseE while another portion is drawn oil into thevessel K. The whole system is maintained under pressure andto maintainthe pressure thevessel is provided with an outlet-pipe closed by highlya valve k'through which a quantity of acid I 1225706) for the oxidationof nitrogen permay be periodically drawn off from the vessel K asafinished product ready for sale. It will be understood that the oxygencommences its circulation through the system in the liquid raiser E. lnraising the mixture of nitric acid and nitrogen tetroxid, the oxygencauses the formation of nitric acid even in the. raising pipe. Thisoxidation is continued inthe tower B, where oxygen and liquid flow inthe same direction and where the oxygen is allowed to act upon a liquidmixture which has already been acted upon by oxygen in the tower A. 'The`action of the oxygen upon the liquid thus ,takes place in stepsaccording to the counter current principle. From the tower B the rest ofthe oxygen passesthrough the pipe H to the liquid raiser E. where it isallowed to act upon the Afresh niixtureof watei or nitric acid. Thisaction is continued in the tower A, where the gas and the liquid How inthe same direction. Owing to the fact that the oxygen is never quitepure, the

oxygen leaving the tower A will be somewhat diluted, and it is necessaryto let out a quantity of gas (corresponding to the content ofimpurities) from the tower A. This takes place through a deplilegmator Owhich effects the condensation of the nitric acid vapors, which arecarried along with the escaping gas, the condensed acid. flowing backinto the pipe Gr. From the mixing tubes m a pipe P leads directly to thetop of the tower A and through this pipe a portion of themixture from mmaybe led directly into the towerA, without passing through the liquidraiser E. Another pipe R connects the pipe C directly to the top of thetower B, so that it is 'possible to pass a portion of liquid directlyfromtlie pipe Cinto the tower.

Contrary to the known processes (cfr. for instance German patentspecification No.'

oxid to nitric acid under normal temperatures or a temperature loweredto about 0 C. by' Ineansof cooling are employed, according to thepresent invention the most favorable results are obtained by highertemperatures (about 70 C. having pressure in which proved to besuitable). For this reason the the first instance nitric oxid NO and inthe process is advantageously carried into effect by means ofnitrogenoxids ina gaseous state as obtained for instance in the manufacture ofnitrate from nitrite and nitric acid or by boiling nitrosylsulfuric acid(in second instance nitrogen trioxid Y N203). The conversion of theseoxids to liquid nitrogen peroxid is effected as known byv a stronglyexothermic oxidation reaction and the manufacture of vperoxid thereforeinvolves the use of cooling means.

According to the present process the heat spaces considered order ofsuccession to thatV` of the dilute oxids, oxygen produced by theoxidation of the nitrogen oxids is utilized for the process and it hasbeen found, that in this manner so much heat is evolved in the apparatusthat indirect heat supply can be avoided, which on its side` involves asimplification of the apparatus. V'

The process vantage in so far as the disadvantages and expensesconnected with the manufacture of liquid nitrogen peroxid are avoidedbut a considerable saving is also attained as re gards the constructionand working of the plant. ln carrying out the process in the describedmanner the oxygen is completely utilized. As yresidual gas is obtainedonly the small quantities of impurities whichis is therefore not only ofadalways contained in the oxygen employed,

mixed with nitrogen oxids. This residual gas can be utilized byabsorption in water or in alkalis or in other ways.

As a matter of course the apparatus could be supplied with nitrogenperoxid in a liquid state.

)Ve claim- 1. Process for the manufacture of concenf trated nitric acidwhich consists in maintaining currents of a nitrogen oxid, oxygen and anaqueous reaction with each other through a series of reaction spacesunder a superatniospheric pressure,

- the current of oxygen being caused to pass in parallel to the aqueousreaction liquid `through each of rthe individual reaction spaces,whereas the oxygen is supplied to the series of reaction spacesconsidered as a unit in thefreversed order of succession to that of thereaction liquid.

2. Process for the manufacture trated nitric acid which taining currentsof a nitrogen oxid, oxygen and dilute nitric acid in contact with eachother through a series of reaction spaces vunder a superatmosphericpressure, rent of oxygen being caused to pass in parallel to the dilutenitric acid through eac-h of the individua-l reaction spaces, whereasthe oxygenis'supplied to the series of reaction as a unit in thereversedof concenplied. to the series of reaction spaces con sidered asa yunit in the reversed order of succession to that of the reactionliquid.

consists in mainthe cur-l -liquid in contact -taining currentsof anitrogen oxid, oxygen and an aqueous liquid in contact with each otherthrough a series of reaction spaces under a superatmospheric pressureand at n raised temperature, the current of ozygen being caused to passin parallel to the aqueous nreaction liquid through euch of theindividua-1 reaction spaces, Whereas the oxygen is supplied to th`e'series of reaction spaces 4considered as a unit in the reversed orderof succession to that of the reaction liquid. In testimony that Weclaim'the foregoing as our invention, We have signed our names I5 y in'presence of two subscriblng witnesses.

EINAR BERGVE.

` OLAF JENSEN.

Witnesses:

C'. NORMAN EINAR N. Ynnsnlinirru).

